Why does cutting an onion make you cry or sting you eyes?

Answer 1

Onions cells contain traces of sulfur, that are broken and released into the air when cut. These sulfured compounds react with the moisture in your eyes forming sulfuric acid, which cause the burning sensation you feel. The defense mechanism of the eye is to create tears to dilute the acid. So your tears protect your eyes from damage.

So to answer both your questions:

1. The stinging feeling is caused by sulfer from the onion cell
2. The tears are a defense mechanism to protect your eyes from potential damage.

Answer 2

When you cutting Onion. You can smell and it will making you cry by your eye. Onion will went into the air and it possible to damage the eye. Eye have to start cry to protect against Onion Air. If you putting your hand into your eye with Onion Raw on hand and It will tear or sting your eye.

Answer 3

I haven't read anything about onions and crying from them, but I've read some of the answers here and agree that there are vapors of some sort given off from the onion which make you cry. However, I've personally found that crying isn't necessarily from the vapors hitting your eyes. Instead, it affects your sense of smell. For years, I've avoided breathing thru my nose while cutting an onion, and never cry when doing this. I breathe thru my mouth only. Try it, it works. But keep this in mind, once you breathe in thru your nose just once, and breathe in the onion vapors, you more than likely will begin to cry.

Answer 4

I just learned about this in organic chemistry this semester. Onions contain a type of molecule that turns into a lachry-mator (pronounced lack-ra-mater) that irritates the eyes and causes tear production and irritation. Although scientists are unsure why the lachrymator causes irritation, they suspect that the fact that one of the products of its breakdown is sulfuric acid. Keeping onions under water while chopping them will help with the irritation because the lachrymator is washed away by the water. Also, chopping it while it is still cold will help because the lachrymator cannot escape and become airborne as easily if the onion is cold.
Smoke has a lachrymator in it, and so does tear gas.

Answer 5

As you cut the onion, onion cells are broken -> releases aliinases, an enzyme that breaks down sulfides to form sulfenic acid -> sulfenic acid breaks down in the air to form a gas -> gas reaches the eye and reacts with water to form sulfuric acid -> the acid irritates nerve endings in the eye -> tear is produced to flush them out.

Answer 6

the "gas" releiaved when cutting onions is SH which combines with the water in your eye and nostrils to sulfuric acid - which makes them tear. Just rinse in cold water before cutting^^

Answer 7

this is the basic of chemical warfare, animals can defend themselves from predators. but, most plants can not. when the skin of an onion is broken it releases to chemical compounds that when combined with moisture from your eyes creates sulphuric acid.

Answer 8

I have read that something in the vapors interacts with the tears to make an acid, and that's what stings.

Answer 9

A chemical is released to try and stop you from cutting into it. Many plants release chemicals when they're "attacked".

Answer 10

http://answers.yahoo.com/question/index;_ylc=X3oDMTFtMXI2N3ZvBF9TAzI3MTYxNDkEX3MDMzk2NTQ1MTAzBHNlYwNmcm9udCBwYWdlBHNsawNGUC1Ub2RheUludA--?qid=20061205154802AAQtXc0&fr=hp

how to cut it without crying:

http://answers.yahoo.com/question/index;_ylc=X3oDMTFtMXI2N3ZvBF9TAzI3MTYxNDkEX3MDMzk2NTQ1MTAzBHNlYwNmcm9udCBwYWdlBHNsawNGUC1Ub2RheUludA--?qid=1006052642837&fr=hp